1. Field of the Invention
The present invention is concerned with a method of forming etch-resistant polymeric resists for use in the creation of micron and submicron dimension patterns and fine lines. These etch-resistant polymeric resists find use in fabrication of complex structures such as those in electronic devices and magnetic thin film heads.
2. Background Art
Many of the recent advancements in electronic devices and components have resulted from improvements in manufacturing techniques. Some of the most important improvements have occurred in microlithography and in methods of transferring the patterns used to create the complex structures within the electronic devices.
One of the preferred methods of transferring patterns of micron and submicron dimensions is dry etching. This method utilizes plasma or reactive ion etching to remove specific areas of material on a surface so that a pattern remains. In many instances, this method of pattern creation has replaced conventional processes which use solvent development of a material to create a pattern. The solvent development or wet processing techniques frequently do not permit the dimensional control desired in the creation of micron and submicron dimensional patterns; the dry etching techniques do permit such dimensional control.
The material to be dry etched to create the pattern is often a polymeric material due to ease of use, material properties, and cost considerations. When an organic polymeric material is used, dry etching can be done using an oxygen plasma or oxygen reactive ion etching. Upon exposure to an oxygen plasma or to oxygen reactive ion etching, the organic content of the polymer is converted to gaseous forms which are easily removed. In order to create the pattern, there must be some areas of the polymeric material which are resistant to oxygen plasma or oxygen reactive ion etching and other areas of the polymeric material which are not. A preferred method of producing an etch-resistant polymeric material is to utilize a polymeric resist material containing silicon in a sufficiently large quantity so that exposure to oxygen plasma, for example, results in formation of silicon oxides (which form a protective layer to prevent the conversion to gaseous form of organic materials beneath). Metals other than silicon, which are capable of forming protective oxide layers, can be used as well.
Examples of silicon-containing copolymers, comprising a compound containing an acrylate moiety and a siliconcontaining oxime ester of methacrylic acid, which act as a positive resist and which can be dry developed are disclosed in U.S. Pat. No. 4,433,044 to Meyer et al. A method of selectively removing a portion of a layer of material on a substrate by oxygen plasma etching, utilizing a mask of resist material comprising a poly (silane sulfone) copolymer is disclosed in U.S. Pat. No. 4,357,369 to Kilichowski et al. A method of producing solid state devices by dry etching of a resist film comprising a silicon-containing or nonsilicon-containing but organometallic monomer-containing polymer is described in U.S. Pat. No. 4,396,704 to G. N. Taylor.
Another method for forming a micropattern using a technique similar to those above is disclosed in U.S. Pat. No. 4,430,153 to Gleason et al. The method involves forming an etch barrier in the reactive ion etching of an aromatic polyamic acid/imide polymer. The method comprises: coating a surface with a layer of an aromatic polyamic acid; at least partially curing the layer of aromatic polyamic acid to the corresponding aromatic poly-imide; in situ converting the surface layer of the aromatic polyimide to a silicon-containing alkyl polyamide/imide; applying, exposing, and developing a layer of photoresist over the silicon-containing alkyl polyamide/imide, to selectively expose a portion of the silicon-containing alkyl polyamide/imide surface layer; reactive ion etching the exposed portion of the surface layer of the silicon-containing alkyl polyamide/imide with carbon tetrafluoride to remove the exposed portion of the silicon-containing alkyl polyamide/imide surface layer; and subsequently using the oxygen-etch-resistant, silicon-containing polyamide/imide polymer as a mask in processing of underlying layers which can be oxygen reactive ion etched.
Another method for forming a micropattern using a technique similar to those above is disclosed in U.S. Pat. No. 4,426,247 to Tamamura et al.. This method comprises the steps of forming an organic polymeric material layer on a substrate, forming a silicone layer on the organic polymeric material layer, selectively irradiating a surface of the silicone layer with a high-energy beam, exposing the surface of the silicon layer to a radical addition polymerizable monomer gas so as to form a graft polymer film on an irradiated portion of the surface of the silicon layer, performing reactive ion etching using the graft polymer film as a mask so as to form a silicon pattern, and performing reactive ion etching using the silicone pattern as a mask to protect underlaying organic polymeric layers, so as to form an organic polymeric material pattern.
Recently, processes have been developed which permit selective conversion of portions of a non-silicon-containing resist to a silicon-containing etch-resistant resist. The non-silicon-containing resist is exposed to patterned radiation to create a latent image within the resist. The latent image within the resist is then reacted with an organometallic reagent to incorporate an oxide-forming metal such as silicon into the image. The "siliconized" latent image is then dry developable, and the etch-resistant images, as well as underlaying organic polymeric material, can then be dry etched using an oxygen plasma to simultaneously develop and transfer the pattern through to a non-organic substrate below. Examples of this latter method of obtaining dry-developable multilayer resists are described in U.S. patent applications Ser. Nos. 609,690 filed May 14, 1984, U.S. Pat. No. 4,552,833, 679,527, filed Dec. 7, 1984 and 720,781, filed Apr. 8, 1985 (assigned to the assignee of the present invention). The disclosures of these three U.S. patent applications are incorporated by reference herein. Note that the metallic portion of the organometallic material can be selected from Group III A metals, Group IV A metals, Group IV B metals, and Group VI B metals. Examples of Group IV A metals are tin, germanium, and silicon. Examples of Group IV B metals are titanium and zirconium. Examples of Group VI V metals are tungsten and molybdenum. An example of a Group III A metal is aluminum. The preferred metallic portions are titanium, silicon, and tin, with the most preferred being silicon.
However, the methods of creating dry-developable multilayer resists described in the three U.S. patent applications above provide a negative tone pattern, and many practitioners within the electronics industry prefer to use a positive tone pattern. (A negative tone pattern is obtained when the portion of the resist exposed to the patterned radiation remains after development of the pattern; a positive tone pattern is obtained when the portion of the resist exposed to the patterned radiation is removed during development of the pattern.)
In addition, the first two methods, described in applications Ser. Nos. 609,690 and 679,527 preferably utilize polymeric materials which initially do not contain any reactive functional groups such as hydroxyl, amine, carboxyl, phenol, or imide NH, which are capable of reacting with an organometallic reagent. The reactive functional groups are created within the polymeric material using irradiation, photoactive compounds which are added to the polymeric material which subsequently react with the polymeric material after exposure to radiation, and combinations thereof. These methods encounter difficulties on application to novolak resist materials of the type most commonly used in electronics industry lithography.
In order to alleviate the difficulties referred to above, and enable the creation of positive tone resist patterns as well as negative tone resist patterns, an additional method was developed. The additional method provided for wet development of the latent image created within the resist upon exposure to patterned radiation, with subsequent processing to render the resist material remaining after development etch resistant. The etch resistant resist material could then be used to transfer the pattern to underlaying polymeric layers. This method is disclosed in U.S. patent application Ser. No. 713,370, filed Mar. 19, 1985 assigned to the assignee of the present invention, and incorporated herein by reference.
In view of all of the above methods, there remains a need for a method of producing etch-resistant positive tone resist patterns using only dry development techniques. In addition, a simple method of achieving image reversal (the ability to alter the pattern created from positive to negative tone, or the reverse) would be highly desirable.